Non-Pressurized Aircraft Cruise
05-25-2019, 03:47 PM
#1
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Non-Pressurized Aircraft Cruise
Looking for opinions... I'm sure there are many here.
Say you are going to fly single-pilot in an unpressurized aircraft and you will spend upwards of 2 hours at cruise. Let's assume it is fully IFR capable.
You have an oxygen system, but no emergency backup oxygen.
How high are you willing to cruise for 2 hours on your O2 system with no backup?
Say you are going to fly single-pilot in an unpressurized aircraft and you will spend upwards of 2 hours at cruise. Let's assume it is fully IFR capable.
You have an oxygen system, but no emergency backup oxygen.
How high are you willing to cruise for 2 hours on your O2 system with no backup?
05-25-2019, 05:13 PM
#3
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I did 14k for 30 minutes when much younger with no O2. Was not really pleased with my cognitive performance flying the plane.
So I would either want the ability to quickly descend to 12k, or if limited by IFR and MEA, would want a backup O2 system. I wouldn't want to get stuck in the teens with no O2 in some kind of crisis.
So my issue wouldn't really be how high, it would be how soon I could get back down.
So I would either want the ability to quickly descend to 12k, or if limited by IFR and MEA, would want a backup O2 system. I wouldn't want to get stuck in the teens with no O2 in some kind of crisis.
So my issue wouldn't really be how high, it would be how soon I could get back down.
05-25-2019, 09:37 PM
#5
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Also, fitness and conditioning play a big role. I used to cruise at 10-12 without O2 all the time, sometimes higher going through passes up at 13 and 14 and for maneuvers, and with O2 for cruising in higher teens. No issues, but I lived at high alt and was very active.
I wouldn't jump in a plane now and go cruise at 12K w/o O2 for hours, I'm even more fit, but I'm not used to the higher altitude anymore due to living at sea level. I've seen plenty of people get woozy at the higher altitudes, enough that I wouldn't trust them to spend a few hours there. That's one thing I see occasionally with instrument pilot's XC planning, that they've planned some route where they'll be up at 12K for a few hours with no regard to the O2 saturation that they'll be encountering.
I wouldn't jump in a plane now and go cruise at 12K w/o O2 for hours, I'm even more fit, but I'm not used to the higher altitude anymore due to living at sea level. I've seen plenty of people get woozy at the higher altitudes, enough that I wouldn't trust them to spend a few hours there. That's one thing I see occasionally with instrument pilot's XC planning, that they've planned some route where they'll be up at 12K for a few hours with no regard to the O2 saturation that they'll be encountering.
05-25-2019, 09:43 PM
#6
Get me outta here...
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BadFlaps: you cannot prove a thing!
Rick: excellent consideration.
John/James: I should clarify that it would be an oxygen mask with the ability to go 100%, nearly identical in capability to what you would find in a military jet like a T-38.
My concern is: what if the O2 system fails? Yes, it is unlikely... but at some point, that failure is probably catastrophic, unless there is a backup you can use. Or unless you recognize it quickly, and can descend (as Rick says) before you become unable to function.
So, even if you had 100% O2 and a mask (but no backup), would you go to FL200? FL250?
Or would it depend on the answer to Rick's question: how quickly can I descend?
Thanks for the comments. It helps immensely.
Rick: excellent consideration.
John/James: I should clarify that it would be an oxygen mask with the ability to go 100%, nearly identical in capability to what you would find in a military jet like a T-38.
My concern is: what if the O2 system fails? Yes, it is unlikely... but at some point, that failure is probably catastrophic, unless there is a backup you can use. Or unless you recognize it quickly, and can descend (as Rick says) before you become unable to function.
So, even if you had 100% O2 and a mask (but no backup), would you go to FL200? FL250?
Or would it depend on the answer to Rick's question: how quickly can I descend?
Thanks for the comments. It helps immensely.
Last edited by HuggyU2; 05-25-2019 at 10:01 PM.
05-25-2019, 10:22 PM
#7
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Originally Posted by HuggyU2
So, even if you had 100% O2 and a mask (but no backup), would you go to FL200? FL250?
05-26-2019, 07:04 AM
#8
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Was doing a 3+ hour flight at FL410 in the Phenom 300 one time. Got up to go to the lav and the F/O pulled out his mask and hit the test button. Silence. We pulled the hose all the way out, made sure no kinks or anything. Tested it a number of times, thumped it once or twice. Nada. We still had around 90 minutes to go and were over a remote area of Wyoming. I asked him what he wanted to do and he said just press on to SoCal so we did with the understanding if the pressurization system did anything the slightest bit unusual we were heading down in a hurry.
With smaller unpressurized planes you're usually not that far from being at 10k, if the MEA is higher then you're in the mountains and can probably get to lower ground pretty quickly.
With smaller unpressurized planes you're usually not that far from being at 10k, if the MEA is higher then you're in the mountains and can probably get to lower ground pretty quickly.
05-26-2019, 07:08 AM
#9
Disinterested Third Party
Joined APC: Jun 2012
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Originally Posted by AirBear
I asked him what he wanted to do and he said just press on to SoCal so we did with the understanding if the pressurization system did anything the slightest bit unusual we were heading down in a hurry.
What's your time of useful consciousness (TUC) at FL410?
What's your descent time to 14,000 or lower?
(hint: it's longer than your TUC)
No oxygen flow...normally a preflight check? What do you use during an onboard fire or smoke in the cockpit?
05-26-2019, 07:53 AM
#10
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AirBear, great scenario for all of us to learn from. Wondering what
the aeronautical decision making process looked like? Were other
alternatives considered? Why did you ultimately decide to accept that high level of risk? As JB pointed out, Time of Useful Consciousness at FL410 is less than the time it would take to do an emergency descent.
the aeronautical decision making process looked like? Were other
alternatives considered? Why did you ultimately decide to accept that high level of risk? As JB pointed out, Time of Useful Consciousness at FL410 is less than the time it would take to do an emergency descent.
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